The acid and alkaline phosphatases, inorganic pyrophosphatases and phosphoprotein phosphatase of bone. II. Distribution in subcellular fractions of bone tissue homogenates and structure-linked latency

Abstract

1. 1. In subcellular fractions of bone homogenates, obtained by differential centrifugation, the distribution patterns of phosphoprotein phosphatase (phosphoprotein phosphohydrolase, EC 3.1.3.16), acid inorganic pyrophosphatase, acid β-glycerophosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.2) and of various other acid phosphatase activities are closely similar to those reported by G. Vaes and P. Jacques ( Biochem. J. 97, 389–392 (1965)) for the other acid hydrolases of this tissue. The highest specific activity of these enzymes is found in the light-mitochondrial fraction. The highest specific activity of alkaline inorganic pyrophosphatase and of various other alkaline phosphatase activities (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) is found in the microsomal fraction. 2. 2. In cytoplasmic extracts of bone, the various acid phosphatase activities occur in latent form to the extent of 50–60% of their total activity. The latent enzymes are unmasked by a number of treatments (Triton X-100, Ultra-Turrax, low osmotic pressure, freezing and thawing) that unmask the lysosomal β-glucuronidase (EC 3.2.1.31) in a closely parallel manner. 3. 3. These results support the concept of an association of phosphoprotein phosphatase, acid inorganic pyrophosphatase, acid β-glycerophosphatase and the other acid phosphatase activities with lysosomes in bone. Alkaline inorganic pyrophosphatase and the other alkaline phosphatase activities are largely attached to microsomal elements.